The present invention is generally directed to air cooling systems for electronic equipment. More particularly, the present invention is directed to a method and apparatus which enable air-cooled electrical systems to be upgraded in the field in ways which increase their power demands and concomitant heat generation capability while at the same time providing increased cooling capacity. Even more particularly, the present invention enables field upgradability of air cooled computer systems when higher computing power and/or higher power dissipation cards or modules are added to the system.
In one computer system design of interest herein, printed circuit cards are affixed to two sides of a planar circuit board. These electronic components are contained within a cabinet or housing which has an inlet and an exhaust for the passage of cooling air. Also provided in the cabinet is a blower (or more generally, an air-moving device (AMD)) which draws air in through the inlet, through a first set of spaced-apart printed circuit cards, through the blower itself and thence, through a second set of spaced-apart printed circuit cards before the heated air passes to the exhaust vent or port. Such systems are said to operate in a push/pull mode. In this design, the blower is located in the center of the cooling air flow path which is contained entirely within the original housing. In this design, the air that passes over the first set of electronic printed circuit cards on the inlet side is heated and, thus, the air that passes over the second set of printed circuit cards has already been, at least somewhat, preheated. Since thermodynamic heat transfer depends on temperature differences, it is therefore seen that the heat removal capacity for the second set of printed circuit cards is reduced. Depending upon the power dissipation of the electronic components employed in the system, this is often a perfectly satisfactory arrangement.
However, the present invention is particularly directed to situations in which one wishes to increase the power dissipation of the electronic circuit components. While the present invention is directed to a wide variety of electrical and electronic systems, it is noted that it is particularly applicable to computer systems. For example, in computer systems, it is not uncommon to provide mechanisms for increasing the level of computational power provided in the system. The computational power increase is typically provided in one of several ways. In one mechanism, internal computer clock speeds are increased in frequency. This factor alone results in increased power generation by the components in the computer system. Additionally, more processor units may be included in the computer system. This, also, raises the level of power generation which results in increased heat loading which must be compensated for in order to provide desirable levels of reliability and availability.
Various mechanisms for increasing the heat removal capacity of an air-cooled system include providing either more blowers, more powerful blowers or increasing the power to the air-moving devices which drive the air cooling system. However, all of these methods do result in increased system noise, or at least have the capability of doing so. Additionally, it may not be possible to include larger AMDs within the originally provided housing.
Since it is often possible to upgrade electrical and/or electronic computer systems in the field via the mechanism of adding additional modules or by replacing modules with more powerful modules, it is also very highly desirable to be able to upgrade the air-cooling capacity of the system at the same time and in the same manner, that is, by means of an upgrade which occurs in the field.